The VSL signs were activated in late July 2008, but initial evaluations of the system showed inconclusive effects. Changing site conditions in a work zone made a direct before-and-after evaluation of the system deployed in the field problematic, and some problems with the control algorithm were also noted. Given the difficulties in evaluating the system deployed in the field, a calibrated simulation of the site was constructed to assess the effects of the VSL system on traffic operations and safety surrogate measures.
Work zone lane closures were simulated by removing lanes that were closed because of construction. VSL signs were simulated at the same locations as in the field deployment. As such, the sign locations may not have been optimal for the specific lane closure simulated, but they were chosen to allow for consistency between the field and simulation environments.
The results indicated that the VSL could create substantial improvements in traffic operations provided the demand did not exceed capacity by too large a margin. Further, a cost/benefit analysis indicated that VSL signs may be most appropriate for long-term applications
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